There have been conventionally developed many types of roller bearing cages usable in the rod “big end” of the connecting rod in the engines. An example of conventional bearing cages as stated earlier is disclosed in, for example Japanese Patent Laid-Open No.1996-219149. The prior roller bearing cage is made in a configuration resembling any gate in cross section where the circular inside surface of the roller bearing cage is recessed to form roughly U shape. The prior roller bearing cage is composed of a nearly cylindrical cage made up of axially opposite annular members and pillars integral with the annular members and positioned at regular intervals around the circular surface of the cage to provide pockets, and rollers received in the pockets, one to each pocket. With the prior roller bearing cage constructed as stated earlier, moreover, coining operation is applied to the pillars to make outside retainer projections extending partially into their associated pockets to keep the rollers against falling radially outwards away from the bearing cage. Then, any material removal operation is carried out around the circular outside surface of the cage to erase completely depressions caused corresponding in reverse to the retainer projections, making the radially outside surfaces of the retainer projections very close to the prescribed outside diameter of the bearing cage. Thus, the outside retainer projections to keep the rollers against falling away from the cage are made around the circular outside surface of the cage in a way their outside surfaces fit together the circular outside surface of the bearing cage. Moreover, the pillars of the bearing cage are arranged in such a manner that their outside surfaces are flush with the circular outside surfaces of the annular members across their substantially overall length in the axial direction. The pillars are cut away at their axially middle areas to make the pockets spaced out wide. The outside retainer projections to keep the rollers against outward escape out of the cage are placed in a way lying on the circular outermost surface of the bearing cage. With the prior roller bearing cage constructed as recited earlier, even if the guide surfaces of the bearing cage against which the rollers are carried for rolling motion are somewhat worn away during installation in the engine, the rollers are positively kept against direct engagement with the associated retaining projections, so that the bearing is effectively protected against getting seized up. With the prior roller bearing cage in which the outside retainer projections are made in a way their outside surfaces are flush with the circular outside surface of the bearing cage, the outside retainer projections help increase in area the overall circular outside surface of the bearing cage. Instead, the surface-to-surface contact stress of the bearing cage against any mating counterpart thereof is made reduced so that the roller bearing is kept against seizure. The prior roller bearing cage is designed to carry effectively the loads imposed by modern high-speed engines because of the constructional features as recited earlier.
Another example of the roller bearing cage having a gate-like configuration in cross section is disclosed in, for example Japanese Patent Laid-Open No.1997-236130. The prior needle bearing cage is envisaged ensuring accuracy of the guide surfaces boarding the pockets against which the rollers are carried for rolling motion, even without any subsequent post-working operation, thereby making a further refinement to precision even with production cost savings. With the needle bearing cage recited earlier, the circular surface inside of the bearing cage is made up of inside surfaces of the middles small in thickness, and inside surfaces of the axially opposite sides, which merges together with the middles through ramps inclining towards the axial center of the cage. The guide surfaces around the pockets against which the rollers are carried for rolling motion is constituted with sheared edges lying on the pitch circle distance P.C.D.
Moreover, a prior production method of the roller beating cage is also disclosed in, for example Japanese Patent Laid-Open No.1997-242763 In which the rolling element raceways are made inside the outer ring with using rolling operation. In the prior production method recited earlier, a ring-like blank is heated up to a prescribed temperature to form austenite, and then cooled down at rapid cooling rate. The ring-like blank remaining in austenite is subject to the rolling operation, and thereafter cooled down to a temperature below Ms point where the austenite transforms to form martensite to be hardened to above 57 Rockwell C.
Meanwhile, as the modern engines are remarkably refined in efficiency and performances to get further higher in horsepower, the roller bearing cage for the powerful engines has to be made so as to stand up to further high-speed revolution, even with cost savings and more friendly to environment in the production thereof. The roller bearing cages of the type recited earlier are used extensively for the engines and verified they successfully work with better durability. With the prior roller bearing cage made in a configuration resembling any gate in cross section where a ring-like blank is turned on lathe to cut a circular inside surface of the blank into roughly U-shape in cross section, nevertheless, as the cage would sometime made uneven in thickness, the surface-to-surface contact stress of the bearing cage against the circular surface inside the big-end bore trends to result in any harsh condition during installation in the rod “big-end” of the connecting rod in engines. Further, the turning operation carried out on the lathes to finish the cage blank into the desired contour would take substantial time and effort, while involving cutting much excess metal, in the form of chips, from the cage blank. This means that the prior manufacturing process for the roller bearing cage produces in vain much metal waste in the form of chips or debris, which should be disposed properly. Besides, the prior cages constructed as stated earlier, because of their configuration like any gate having U-shape much bumpy with many angular corners, is very tough to machine them by the turning operation on the cage blank.
The prior needle bearing cage recited earlier, as with the roller bearing cage as stated just above, has the circular inside surface including the inside surfaces of the middles small in thickness and other inside surfaces of the axially opposite sides, which merges together with the middles through ramps inclining towards the axial center of the cage. The cage construction as recited above has an adverse tendency to cause somewhat increased surface-to-surface contact stress that might take place between the bearing cage and the circular inside surface in the big-end bore of the connecting rod. In addition, the prior needle bearing cage constructed as stated earlier is also tough to produce it by the turning operation on the cage blank, because the circular inside surface is made in the angularly bumpy configuration, which consists of the inside surfaces of the middles small in thickness, and other inside surfaces of the axially opposite sides merging together with the middles through ramps inclining towards the axial center of the cage. The prior needle bearing cage is further unsuited to handle it since the cage has no construction favorable for positively retain the associated needles.
The production method of the roller beating cage recited earlier using the rolling operations to manufacture the race ring, because of requiring highly skilled effort of rolling operation, is hard to work the cage with high accuracy in roundness, concentricity, and so on.